1- Copenhagen to Stockholm by AirThere are direct flights available daily for travelers going from Copenhagen to Stockholm, or vice versa. The length of the flight is 1 hour 15 minutes. Depending on the time of year, round trip flight prices from to Stockholm can be down to double digits. A fast option, but involves getting to the airport.
2- Copenhagen to Stockholm by Train
Taking the train from Copenhagen to Stockholm usually costs a little less than getting there by plane but it's a 5 1/2 hour trip. Train tickets are cheaper midweek, and on night trains, while weekends are pricey - no matter if you're going from Copenhagen to Stockholm or the other way. You can get train tickets and prices at RailEurope.com.
3- Copenhagen to Stockholm by Car
If you'd like to rent a car to get from Copenhagen to Stockholm, it's a 7 hour drive (600 km / 370 mi). Follow the E20 across the Øresund Bridge (toll required) to Malmø and on to Helsingborg. From there, take the E4 all the way to Stockholm. To get to Copenhagen, take the E4 to Helsingborg and follow the E20 down to Copenhagen. This is likely one of your slower and cheaper options.